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ORLANDO, Fla. — A gay nightclub in Orlando was the scene early Sunday of the worst terror attack in U.S. history since 9/11.

50 people were killed inside the Pulse club and at least 53 people were injured, police say. The gunman was Omar Mateen of Ft. Pierce, Florida, a law enforcement source told CNN.

Orlando police shot and killed Mateen.

Law enforcement sources told CNN that the suspect had possible explosive devices strapped to his body and in his vehicle, but a U.S. official said later that no explosives were found.

At least nine officers were involved in the shootout, Mina said. Several coroner vans were seen traveling toward the nightclub.

One officer suffered an eye injury when a bullet struck his Kevlar helmet, said Danny Banks, special agent in charge of the Florida Department of Law Enforcement’s Orlando bureau. The helmet saved the officer’s life, Banks said.

Pulse shooting: In hail of gunfire in which suspect was killed, OPD officer was hit. Kevlar helmet saved his life. pic.twitter.com/MAb0jGi7r4

The shooter has been identified as Omar Saddiqui Mateen, 29, of Fort Pierce, about 120 miles southeast of Orlando, two law enforcement officials tell CNN.

Orlando authorities said they consider the violence an act of domestic terror. The FBI is involved. While investigators are exploring all angles, they “have suggestions the individual has leanings towards (Islamic terrorism), but right now we can’t say definitely,” said Ron Hopper, assistant special agent in charge of the FBI’s Orlando bureau.

Authorities are also looking into the possibility the attack was a hate crime, a law enforcement source told CNN.

“It’s appears he was organized and well-prepared,” Orlando Police Chief John Mina said early Sunday. The shooter had an assault-type weapon, a handgun and “some type of (other) device on him.”

Officials, aided by the FBI, warned that a lengthy investigation was ahead, given the number of victims and the scope of the violence.